Batteries mounted as a power source on, for example, an electric motor-operated vehicle include the alkaine secondary battery or the like. When such batteries are used with repeated charge-discharge cycles without using up their battery capacity 100% (rated capacity), the discharge ends as shown in FIG. 3 within a period of time which is shorter than that of previous discharge. In the worst case, the battery voltage reaches a discharge end voltage before discharging almost no charge.
Such a phenomenon in which the discharge comes to an end in a shorter period of time than previously possible when the battery is used with repeated charge-discharge cycles without using up 100% of the battery capacity is known as the memory effect. To avoid such a situation, the battery capacity must be used up almost 100%. Practically the memory effect is reduced by discharging the battery at a relatively small current, for example 0.1 to 0.2 CA.
That is to say, a refresh discharge at a small current should be carried out when the discharge time (usable time of the battery) has become short. However, the decision on the timing when the refresh discharge should be carried out is up to general users and so it is not clear what timing is effective and efficient for reducing the memory effect. As a result, in most cases the refresh discharge is not effective.
The object of the invention made in view of the above is to provide method and device for reducing the memory effect of the battery by carrying out the refresh discharge at an appropriate timing either automatically or manually upon receiving an alarm to reduce the influence of the memory effect effectively and efficiently.